Method of preparing a starch enveloped mineral material



Patented Dec. 13, 1938 UNITED, STATES METHOD OF PREPARING A STAR-OH EN-VELOPED' Harold '1. Ruff, Chlliicothe, Ohio, assignor to The MeadCorporation,

corporation of Ohio No Drawing.

9Claims.

This invention relates to the'manufacture of paper, and moreparticularly to the manufacture of sized and unsized papers, of filledori coated character, such as are particularly useful as printingpapers, or so-called book papers, and

coated papers.

One of the principal objects of the invention veloped filler or mineralmaterial which is of predetermined controlled cluster size.

Another object of the invention is to provide a paper having suchenveloped finely divided mine'ralmaterial of controlled cluster sizedistributed in and/or upon the sheet, and the method of producing thesame.

Another object of the invention is to provide such a paper which will beparticularly free from "dusting" and "picking" on the printing machine95 and the method of producing such paper.

- Another object of the invention is to provide" a superior sized paper.filled with a mineral material which is alkaline, in reaction, and themethod of producing the same.

Still another object is to provide a method, in the manufacture ofpaper, which comprises the preparation and utilization, of a starchsizing material, with mineral filler or coating material, which givesmore economical and superior results in its utilization in the papermaking process, and produces a paper of superior characteristics as touniformity of cluster size and distribution of the filler materialthroughout the sheet, its comparative freedom from dusting and pickingon the printing machine, its comparative freedom from odor and itssuperior color.

As is well known, it has been a practice for many years to size paper tosecure certain desired characteristics in the finished sheet. In

some instances, the sizing material has been added. to the fibrousfurnish before it is fed on to the forming wire, so that the'sizing isaccomplished as a paper sheet is formed; while in other instances theformed sheet is sized, as no for example in so-called "tub sizing" inwhichthe formed sheet is passed through a bath of the size solution orsuspension. A number of materials have been used for sizing, so-calledrosin size being one of the best known., To some llextent starch hasalso been used in sizing; but

Chillicothe, Ohio, at

Application January 25, 1934, Seriai No. 708,250

iii such cases, especially for printing papers, it has beenfound that an-unduly large percentage of starch needs to be used to prevent'dustingand picking of the papers upon printing, which of course has mitigatedagainst such use be- 5 cause of the extra expense involved. Starch hasbeen suggested to some extent as desirable to be used in connection withmineral filler material which is alkaline in reaction. such ascalciumcarbonate. Another difiiculty has been ex- 10 perienced in theutilization of starch in filled papers in that there is ordinarily anuneven distribution of filler particles occasioned by the formation offiller clusters of uncontrolled character when fiocculating agents areadded to the sheets. These varying filler clusters produce a wildformation and result in non-uniformity, with variations in the degree ofopacity and ink receptivity of different parts of the paper.Flocculation is ordinarily necessary with a starch size, when used asabove referred to, to prevent such excess of the high losses of finelydivided filler through the forming wire,'and such fiocculation to avoidthe operating difiiculties and expense results in the seriousdisadvantages in for- 25 mation referred to.

In the manufacture of coated paper's; casein is used almost universallyas a binder or adhesive constituent of the suspension of finely dividedmineral which forms the coating.this suspension being normally referredto as a suspension of "coating color". Casein however is a comparativelyexpensive constituent of the paper. In addition casein ascommercially-available to the paper mill is not at all a uniform 35product and this occasions considerable dimculty in manufacture, as itis well known that very slight changes in constituent characteristics,concentrations, relative concentrations, etc.

will produce marked variations in resulting prod- 0 ucts and thatapparently insignificant changes in the paper making processes andconstituents may cause such wide variations as make the diifer-' encebetween a commercially salable product and one which-is not. Anotherobjection to casein 45 is that when once put into solution by means ofsuitable additive solvents, it cannot be kept for any considerablelength of time but soon decomposes; and in addition it possesses anobjectionable odor whichmakes paper containing it quite undesirable, ifnot entirely. useless, for

wrapping products, such as food products, the taste of which ismaterially afiected by the caseinodors. In addition casein solutionspossess a dark yellowish brownv color which must be offset by the use ofexpensive fillers of unusually high white color where the final whitecolor of paper is of importance.

Despite these objectionable features casein has -been used heretofore,at least for a number oi years, to the practical exclusion of all otherforms of sizing and adhesive materials in the preparation of so-calledcoated papers such as the coated papers which are used to such a largeextent in the present day magazines for color picture reproduction.starches have been generally considered substantially useless as anadhesive in making a coating color suspension.

By meansof the present invention, however, starch can be used withcompletely satisfactory results as the adhesive material for a coatingcolor suspension; and can also be used as an entirely satisfactorysizing material for either a filled or unfilled sheet, with hithertounattained results. A

In the practicing of this invention the starch is intimately admixedwith the finely divided mineral material, in water, to produce anintimate and substantially homogeneous intermixture of the starch andmineral particles, and the suspension is then heated to a temperaturesufficient to cause the starch granules to burst open while in thisintimate and close juxtaposition to the min- 'eral particles, and in sodoing the bursting mateao rial released from the starch granules willint!- mately envelop the mineral particles contiguous to them, and themineral particles will be intimately surrounded and wet by a starchfilm. The result is a suspension of the starch film surrounded mineralparticles which will not be broken by the agitation to which it issubsequently subiected in the paper making sizing and coating processes.a I

As illustrative of a procedure which is satisfactory for the practicingof this invention, two parts of cold water may be added to one part ofstarch in a vessel preferably equipped with high speed stirring or otheragitating device and provided with steam coils or other heating meanssuitable for heating up the water suspension of materials in the vessel."The slurry in the vessel is stirred and three to four parts of finelydivided mineral filler material are added during the stirring, and untilthe mineral material and the starch surround the several particles witha wet starch film. Very satisfactory results will be secured if themixture or suspension is heated to 185 F., by means of steam coils, andmaintained at that temperature while being agitated for about fifteenminutes. During this heating and agitation the starch granules willburst and the resulting wet film coating of the mineral particles willresult. The material within the vessel is then allowed to cool and jell.The jail can then be broken, as by means of a high speed stirrer orother suitable devices and its viscosity thus reduced without destroyingthe homogeneous distribution of the filler particles, within theirseveral starch films, throughout the mass. Also, the jeli having beenbroken the mass can be diluted to any degree desired without appreciablyaffecting the condition of the mineral-starch film particles. Fromexperience in practicing this invention the mass can be diluted almostinfinitely without causing any apparent variation in the condition ofthe the 7 In addition to brealdng the jell down by means of s'tirrers,the same result can be accomplished by centrifugal pumpingof the jelledmass, or by grinding it in a pebble mill, or the like. T

The starch filmed mineral particles are present in an extremely finestate of subdivision, and are held in that condition, and in a state ofextremely uniform distribution. And when added to a paper forming stockor furnish will maintain that uniform distribution and produce anunusually uniform distribution of filler throughout the paper sheet.Where an extreme state of subdivision, such as can be secured under thisinvention, is detrimental because of the resulting filler losses when acomparatively large proportion of the filler suspension material iscarried through the screen into the eiliuent system, this difficulty canbe readily overcome by the addition of suitable amounts of fiocculatingagent. The fiocculating agent can be added in desiredor controlledamounts to give desired or controlled degree of flocculation, and theresulting flocculation will produce substantially uniform results inbuilding up the finely divided filler-starch filmed particles intoclusters or sizes which will also be of quite uniform character. As aresult the size of the clusters thus formed may be readily controlledover a wide range, from practically colloidal size up to quite coarse,readily settling. aggregates or clusters.

The material thus prepared is not only usable for making filled paperbut is especially adaptable for use as a coating color suspension formaking coated paper, such as the coated book paper referred to above.Also, of course, the relative percentage of starch and mineral material,produced,

-may be varied to give the desired characteristics to the paper in whichit is used. The character of the starch used has some appreciableeffect, root starches such as'tapioca and potato starch giving bettersizing efiects than do the cereal starches. The material as thusprepared has most extraordinary characteristics when compared withmixtures of mineral material and starch as prepared in other ways,-orwhen compared withboiled starch"alone. When mineral filler material isadded to boiled starch in quantities large enough to give the necessarycolor and ,opacity, it has been found that either a thick viscous pasteresults, so thick that it will not permit of proper flow or of properapplication and spreading on the paper by usual devices such as are usedin applying coating color to paper, or a fiocculation of the mineralmaterial will occur entirely defeating the desired purpose of use of thestarch as a binding agent. Where a thin mixture was used with a view toavoiding the above .difllculties opacity suifered quite materially, andwhatever resultant coat remained upon the paper as a coat adhered butpoorly, and in the case of filler the filler particles were bound verypoorlyto the paper, with the result that what is known as dusting andpicking were present to an inordinately large degree.

It is not definitely understood just why starchmineral suspensionprepared as above described has these very extraordinary and unusualcharacteristics. In fact, thereis little if any definite information asto the nature of a starch jelly, and as to what changes take place whena jail is formed and when' it is broken down. Furthermore the structureof jells in general is a controversial one in science; but despite thislack of accurate information from the purely scientific point of view,it has been found that when the starch granules are caused to burst whenthus intimately admixed with the finely divided mineral particles the.result is to produce the mineral particle-starch film product which has.

the unusual and extraordinary characteristics herein referred to.

As an example of processing to produce a coating color suspension,satisfactory results have been secured with the following relativeproportions and procedure,120 grams of tapioca starch is first mixedcold with 200 ml. of water.

This cold suspension is then mixed with,400' grams of finely dividedmineral material, such as calcium carbonate, in 1300 ml. of water. Themixture is then heated to 90 centigrad'e and kept at that temperaturefor about thirty minutes. It should then be ground in a suitable way, asin a rod mill or pebble mill for about twenty minutes. This will give afluid coating color sus-' pension which has little or no tendency to.iell on standing. "Aging this coating color at room temperatures fortwenty hours or even more will of the ingredients wh ch go to makeup thepaper in its manufacture are acid in character and therefore of suchcharacter as to react with the alkaline material such as calc umcarbonate A filler-starch film ma erial of the character produced bythis invention completely avoids, these difiicuities which have hretofore been attendantunon the use of alkaline fi ler materials as thematerial roduced acco d n to this nvention. in any dilutions and underany conditions of use whichhave thus far been encountered. is of suchcharacter that the obiectionable react on'between the acid materials.such as Mum and the alkal ne mineral mater al is avoided. As a resultthe control of time of contact as between the acid.

' i 17 b i and alkaline mater al which hag n I of the agglomerates orclusters may be controlled exercised in the commercial o erations hwhich applicant is'associat d is entirel miner-m- 'sary. In fact.whereas i has been the usual nrantice to introduce the alum at therifiies. and lust before the diluted stock-filler susnension g es on to.the forming wire, in order to cut down the reaction period. withfiller-starch suspensions made according to this invention all of theingredients can be introduced into the beater and the question of timeis of no operating consequence. Not only that but through theintroduction of the alum into the beaters flocculation is moredefinitely controlled and consequently losses through the wire into theeffluent system are decreased.

In the making of a coating color suspension good results' can be securedwith the following relative proportions and procedure-400 grams of dryalkaline filler and 200 ml. of water are 'mixed with a suspension of 15-grams of tapioca flour starch in 50 ml. of water. This suspension isthen heated to 90 centigrade and maintained at that temperature for somefifteen to, twenty minutes. The iell is then thinned by suitablemechanical'processing and water added to give a suspension of the properviscosity and containing the desired amount of solids. When dilutedtoviscosity approximating that of the ordinary coating color sus'pensioncontaining casein and the usual amount of solids, the resulting colorcontains approximately 28% of solids.

Such a color suspension when applied to the paper and supercalenderedgave unusually fine results on the standard "pick test. As analternative the mineral-starch film suspension after being thinned by.suitable mechanical processes may have added to it grams of caseindissolved;

in 25 ml. of water containing 6 grams of N82CO3.

As an illustration of procedure in manufacturing book paper of very lowsizing content, the following procedure has been found satisfactory,-asuitable amount of alkaline filler (de-?' pending on the amount offiller desired to be contained in the finished paper sheet) is cookedwith 10% starch at a suitable temperature, the cooked'mixture beingcirculated through a cen trifugal pump to prevent ielling. It hasfbe'enfound that a temperature of 801 C. is usually adequate for causingrupture of the starch granules;

but temperature in excess of that may be used.- 450 pounds of dry weightof this material is added to a 3000 pound beater. be added at the beaterif desired; or no additional alkaline filler need be added except whatis added in the form of broke, and the balance of filler for the sheetmay be added to the wire side of the sheet during the formation thereof,as set out in U. S. Patent to William Edison Bair No. 1,875,208 whichbelongs to the assigneeof the present application. An amount of alumdesired to give the necessary fiocculating efiect, and to thus controlthe amount passing through the wire into the effluent system, may beadded in the riil'ies. Where acarbonate filler is used the alum canstill be added in the beater in such proportion as desired. Increasingthe percent of alum, with the proportions above referred to,-

from 1 to 2% would result in such coarser ag glomerates of thefiller-starch film particles as to cut down the eflluent losses in half.The agglomeratesv so produced while coarser are of clustersizes'substantially uniform, so far as practical results are concerned.and are uniformly distributed in the sheet. And as the size at will bythe addition of alum or other flocculating agent, a sheet may be formedcontaining Alkaline filler can" loidal size, particles to comparativelyquite large clusters.

As an illustration of a rosin sized paper, such as a book paper,manufactured through the util-" ization of the present invention thefollowing proportions and procedure are satisfactory,to a

paper furnish containing approximately 50% soda and 50% sulfite pulps.2% rosin size and 4% a'lum were added in the beater in the usual" Ascompared with the efforts at starch sizing as heretofore practiced, suchas in so-called soft sized sheets, the sizing can be eflected by thepracticing of the present invention with very large savings in theamount of starch,-from 33 to 50% less than when the starch is boiledseparately and then added to the filler as in such instances of use ofstarch. as have heretofore been practiced. And a lower viscosity mixtureis obtained by thepracticing of the present invention than can beobtained by adding the equivalent in sizing of separately boiled starch.Furthermore, when diluted to very low consistencies-forexample to 5% ofsolids-, the suspension of the present invention does not fiocculate andsettle nearly as readily as a suspension made with starch boiledseparately. The mineral-starch film suspension gives a, water suspensionwhich is unusually slow settling com pared with filler in suspensionalone. A starch alkaline material as prepared according to thisinvention may be mixed directly with a solution of casein; and may besized with rosin and alum with practically no loss in sizing efiiciencyor excessive use of alum. Also parafiin may be incorporated in thesesuspensions to, improve the finish of the paper, and to impart increasedink resistance.

While the method and product herein described constitute preferredembodiments of the invention, it is be understood that the invention isnot limited to this precise method and product, and that changes may; bemade therein without departing from the scope of the invention which isdefined in the appended claims.

What is claimed is:

1. The method of preparing a starch enveloped mineral material for useas a filler or coating material or the like in the manufacture of paperwhich consists in mixing starch granules into water to form a starchgranule slurry, adding finely divided mineral material to said starchslurry, stirring the starch slurry and added mineral material todistribute the mineral particles throughout the slurry and effectintimate admixture of the particles andthe starch granules in theslurry, heating said intimate admixture to cause bursting of the starchgranules and liberation of the, starch contents thereof immediatelyadjacent the mineral particles whereby to cause such liberated starchmaterial in the slurry to form upon the mineral particles an envelopingand protecting film and to effect a suspension of such starch filmenveloped particles, cooling such suspension to cause it to jell,

and breaking down such jell by agitation to form a homogeneous, fiowablesuspension of such film enveloped mineral particles and withoutdestroying said film enveloped condition.

2. The method of preparing astarch enveloped mineral material for use asa filler or coating material or the like in the manufacture of paperwhich-consists in mixing starch granules into water to form a slurry,adding approximately two parts water and one part of root starch, addingthree to four parts of finely divided mineral materialtothe slurry,stirringthe starch slurry and added mineral material to distribute themineral particles throughout the slurry and effect intimate admixture ofthe particles and the starch granules in the, slurry, cooking saidintimate admixture 80-90 C. to cause bursting of the starch granules andliberation of the starch contents thereof immediately adjacent themineral particles whereby to cause such liberated starch material 3. Themethod of preparing a starch enveloped mineral material for use as afiller or coating material or the like in the manufacture of pa perwhich consists in mixing starch granules into water to form a. starchgranule-slurry, adding finely divided mineral material to said starchslurry, stirring the starch slurry and added mineral material todistribute the mineral particles throughout the slurry and effectintimate admixture of the particles and the starch granules in theslurry, heating said intimate admixture to cause bursting of the starchgranules and liberation of the starch contents thereof immediatelyadjacent the mineral particles whereby to cause such liberated starchmaterial in the slurry to form upon the mineral particles an envelopingand protecting film and to effect a suspension of such finely dividedstarch film enveloped particles.

4. In the manufacture of paper, the method of preparing a starchenveloped mineral material for use as a filler or coating material orthe like in the manufacture of paper which consists in mixing starchgranules with water and agitating to form a starch granule slurry,adding finely diveded mineral material to said starch slurry whileagitating and continuing the agitation to distribute the mineralparticles throughout the slurry and effect intimate admixture of theparticles and the starch granules in the slurry, heating said intimateadmixture to cause bursting of the starch granules and liberation of thestarch contents thereof immediately adjacent the mineral particleswhereby to cause such liberated starch material in the water to formupon and about the mineral particles an enveloping and protecting filmand to effect a suspension of such starch film enveloped particles.

which consists in mixing starch granules into water to form a slurry,adding finely divided mineral material to said starch granule slurry,stirring the starch slurry and added mineral material to distribute themineral particles throughout the slurry and effect intimate admixture ofthe particles and. the starch granules in the slurry, heating saidintimate admixture to cause bursting of the starch granules andliberation of the starch contents thereof immediately adjacent themineral particles whereby to cause such liberated starch material toforfn upon the mineral particles an enveloping and protecting film andto efiect a suspension of such starch film enveloped particles, coolingsuch suspension to cause it to jell, breaking down such jell by highspeed agitation to form a homogeneous, fiowable suspension of such filmenveloped mineral particles and without destroying said film envelopedcondition, and diluting such fiowable suspension of film envelopedparticles for use as a filler material or the like in paper making.

6. The method of preparing a starch enveloped mineral material for useas a filler or coating material or the like in the manufacture of paperwhich consists'in mixing starch granules into water to form a slurry,adding finely divided carbonate mineral material to said starch granule.slurry, stirring the starch slurry and added mineral material todistribute the mineral til particles throughout the slurry and efl'ectintimate admixture of the particles and'the starch granules in theslurry, heating said intimate admixture to cause bursting or the starchgranules and liberation of the starch contents thereof immediatelyadjacent the mineral particles whereby to cause such liberated starchmaterial in the slurry to form upon the mineral particles an envelopingand protecting film and to efiect a suspension of such starch filmenveloped'par- 'ticles. I

7. The methodof preparing a starch enveloped mineral material for use asa filler or coating material or the like in the manufacture of paperwhichyconsists in mixing starch granules into water to form a slurry,adding finelydivided carbonate mineral material to said starch granuleslurry, stirring the starch slurry and added mineral material todistribute the mineral particles throughout the slurry and effectintimate admixture of the particles and the starch granules in theslurry, heating said intimate admixture to cause bursting of the starchgranules and liberation of the starch contents thereofimmediatelyadjacentthe mineral particles whereby to cause "suchliberated starch material to form upon and about the mineral particlesan enveloping and protecting film and to eiIect a suspension of suchstarch film enveloped particles, cooling such suspension to cause it toJell, and

breaking downsuch :Iell by high speed-agitation to torma homogeneous,flowable suspension of a such film enveloped mineral particles andwithout destroying said film enveloped condition. 8. The method orpreparing a starch enveloped mineral material for use as a filler orcoating material or the like in the manufactureoi paper which consistsin mixing approximately onepart'ot starch granules into two parts orwater to form a starch granule slurry, adding three to four parts i offinely divided mineral material to said starch slurry, stirring thestarch slurry and added mineral material to distribute the mineralparticles throughout the slurry and eirect intimate ad- 'veloped mineralparticles mixture or theparticles and'the starch granules in the slurry,heating said intimate admixture to a temperature of substantially 80-90C. to cause bursting of the starch granules and liberation of the starchcontents thereof immediately adjacent the mineral particles whereby tocause such liberated starch material in the slurry to. form upon themineral particles an enveloping and protecting film and to efiect asuspension of such starch film enveloped particles, cooling suchsuspension to cause it to jeli, and breaking down such jell by highspeed agitation to form a homogeneous,

fiowable suspension 0! such film enveloped mineral particles and withoutdestroying said film enveloped condition. I I

9. The method of preparing a starch enveloped mineral material for useas a filler or coating material or the like in the manufacture of paperwhich consists in mixing starch granules into water to form a slurry,adding finely divided" mineral material to said starch granule slurry,stirring the starch slurry and added mineral ma- Fermi to distribute themineral particles throughout the slurry and effect intimate admixture ofthe particles and the star-ch granules in the slurry, heating saidintimate admixture to cause bursting of the starch granules andliberation ofthe starch contents thereof immediately adjacent themineral particles whereby to cause such liberated starch material toiorm upon the mineral particles an enveloping and protecting film and toeflect a suspension of such starch film envelope'd particles, coolingsaid suspension to cause it to jail, breaking down such :Iell by highspeed agitation to form a homogeneous, fiowable suspension or such filmenveloped mineral par-' ticles and without destroying said filmenveloped condition, film envelopedeparticles for use as afiller-material or the like in paper making, and adding a fiocculatingmaterial to the diluted'fiowable suspension to cause agglomeration ofsaid film eninto clusters. HAROLD '1. non,

diluting such flowable suspension of

